Manfuacture of electrical resistances



1947' I w N. F. ROBBIE ET AL -Y 2,43 ,965

MANUFACTURE OF ELECTRICAL RESISTANCES v Filed Sept. 13, 1944 v 2 Sheets-Sheet 2 Patented Dec. 2,1 94? I MANUFACTURE OF ELECTRICAL assrs'rsnoas Norman Francis Robbie and Eric Horne Whitfield, Welwyn Garden City, England, assignors I to Welwyn Electrical Laboratories Limited, Welwyn Garden City, England, a British company Application September 13, 1944, Serial No. 553,934 In Great Britain Mareh 20, 1944 This invention consists of improvements in or relating to the manufacture of electrical resistances and has particular relation to the method and arrangement for building up insulated resistors such'as are used in wireless equipment and similar circuits. The invention is particularly applicable when the resistor is coated externally with a vitreous enamel and the invention may be used with advantage in making miniature resistors such as are needed in midget radio equipment.-

One object of this invention is to provide an insulated electric resistance element in which a core of insulating material such as unglazed porcelain is provided with a resistance winding and with metallic end connections and with enamel coatings which enclose the resistance windings but leave certain parts of the end connections exposed. A further object is to provide such an insulated electric resistance element in which the point of junction of the resistance winding with each metallic end connection is enclosed in enamel. A further object is to provide, a method of production of insulated resistance elements which on the one hand allows for correct determination of the electric resistance of the resulting element but on the other hand is appropriate to mass production.

This invention comprises a method of making an insulated electric resistance element in which a. core of insulating material such as unglazed porcelain is provided at each end with a metallic end connection, a first mobile, insulating, setting coating-is applied to the core and allowed .or caused to set leaving parts of the end connections exposed, resistance wire is wound on said first coating and conductivel joined to said exposed parts of the end connections and a second mobile, insulating, setting coating is applied to the core over the resistance wire and allowed or caused to set. Subsequent coatings if necessary are applied in the same manner such that all parts with the exception of the axial extensions of the end connections are completely covered and insulated by the insulating coating.

The mobile, insulating, setting coating preferred is vitreous enamel which requires to be fired to cause it to set, but other cements or plasticsin a mobile or semi-liquid state may be used to make the coatings and may be allowed or caused to set by the procedure appropriate to the nature of the coating.

In making resistance elements, especially miniature resistors, it is desirable to use as much as possible of the length of the core forthe resistance wire and to use as little as possible of 8 Claims. (01. 201-47) 2 the length of the core for the external metallic connections. his a feature of this invention that the insulating core may be tubular.

According to a preferred form of this invention the method of making an insulated electric resistance as above indicated includes the use of a metallic end connection having one protuberance engaging in or sprung'into the hollow end of the core and one protuberance projecting in a radial plane to receive the adjacent end of the resistance wire (when applied).

The nature of this invention and of subsidiary features thereof will be appreciated from the following description of typical examples, reference being made to the accompanying drawings in which:

Figure 1 is a side elevation, and

Figure 2 an end elevation of the first form of core; a

Figure 3 is a side elevation, and

Figure 4 an end elevation of'a second form of core;

Figure 5 is a side elevation, and

Figure 6 an end elevation of one form of metal- 110 end connection;

Figure 7 is a side elevation, and

Fi ure 8 an end elevation of another form of metallic end connection;

Figure 9 is a side elevation,

Figure 10 an end elevation, and

Figure 11 a plan of a third form of metallic end connection;

Figure 12 is a side elevation,

Figure 13 an end elevation,

Figure 14 a plan of a fourth form of metallic end connection;

Figure 15 is a side elevation,

Figure 16 an end elevation, and

Figure 17 a plan of a fifth form of metallic end connection;

Figure 13 is a side elevation, partly in section, and Figure '19 is an end elevation of one arrangement of core and metallic end connection;

Figure 20 is a side elevation, partly in section, and

Figure 21 is an end elevation of another form of core and metallic end connection;

Figure 22 is a side elevation, partly in section, and

Figure 23 is an end elevation of a thrd form of core and metallic end connection, and

Figure 24 is a side elevation partly in section of the end portion of the assembly when one coating of enamel has been applied and the resistance wire has been wound on; and

Figure 25 is a side elevation of the same end portion when the radial protuberance of the metallic end connection has been folded down and the assembly is ready for a further enamel coating or coatings.

Figure 26 is a side elevation of the completed article.

Referring to Figures 1 to 4, a tube i2 of ungiazed porcelain has a chamfer I 3 at each end. In Figures 1 and 2 there is also a transverse slot or kerf II at each end.

Referring to Figures 5 and 6, I5 is a metal strip and I6 is a smaller metal strip welded to i! nea its end at right-angles. 5

Referring to Figures 7 and 8, I! are two metal wires side by side and I6 is a metal strip welded to I! near the end and at right-angles.

Referring to Figures 9, and 11, i5 is a metal strip and I8 is a smaller metal strip spot-welded axially on to the end of i5 and bent to provide an external protuberance and also a resilient loop.

Referring to Figures 12, 13 and 14, I! are two metal wires side by side, and I9 is a smaller metal strip spot-welded thereto at the end and bent to provide an external protuberance and also a resilient loop.

Referring to Figures 15, 16 and 17, I5 is a stout metal strip which is bent at its end 20 through an angle of 180. and 2i is a smaller metal strip spot-welded to the end 20.

Referring to Figures 18 and 19, the metal wires I'I slightly splayed outward at the end are inserted in the bore of the core i2 to make a slight grip therein and the small strip i6 lies in the slot [4. The end connection shown in Figures 5 and 6 may be similarly applied to the core.

The 'metal used for the strips or wires may be n ckel-chromium alloy or other suitable material. Referring to Figures 20 and 21, the metallic end connection shown in Figures 9 to 11 or 12 to 14 is inserted in the bore of the core l2 of Figures 3 and 4 and the projecting strip I9 is. bent to lie along the face of the chamfer i3.

Referring to Figures 22 and 23, the metallic end connection shown in Figures 15 to 17 is inserted in the bore of the core I! and the projecting strip 2| is bent to lie along the face of the chamfer l3.

In'manufacturing the resistor the assembly as shown in Figures 18 and 19 or in Figures 20 and 21 or in Figures22 and 23 is dipped into vitreous enamel in a liquid or mobile state. This has two effects. It imparts a coating of vitreous enamel 22 over the surface of the core and the enamel also penetrates into the ends of the hollow core. Firing solidifies the enamel and locks the end connection in position. The reistance wire 23 of appropriate resistance is then wound on to the core l2 (which may be provided with a helical-groove) and the ends of the resistance wire 23 are electrically welded to the projecting strips l6 as shown in Figure 24. The projecting strips l6 are folded snugly down as shown in Figure 25. The assembly is again dipped into the enamel in a mobile condition and a second firing and/or subsequent firings complete the insulation. As shown in Figure 26, the result is to give an outer coating 24 to the resistor and the end connections l5 or H are then hard soldered or welded to the terminals 25 which may conveniently be of tinned copper wire or strip.

4 We claim: 1. The method of making an insulated electric resistance element which comprises the fol-n lowing steps, providing some of insulating material having recesses in each end, wedgingly engaging one end of a metallic end connection within each of said recesses. applying a first mobile insulating setting coating to the core and the greater portions of the end connections leaving certain parts of the latter exposed, setting and thus hardening the coating, winding resistance wire on said core upon the hardened first coating, conductively joining said wire to the uncoated parts of the end connections, applying a second mobile insulating setting coating to the core, the first coating, the resistance wire, and

the end connections, and setting said second coating. I

2. The method of making an insulated electric resistance element which comprises the following steps, providing a tubular core of insulating material, wedgingly engaging one end of end connection elements within the open ends of said core each with a portion projecting radially therefrom, applying a first mobile insulating setting coating leaving parts of said end connection elements exposed, setting and thus hardening said first coating, winding resistance wire on said first core upon the hardened coating and conductively joining it to the exposed parts of the radially extending portions of said end elements, folding said radially extending parts and -joined portions of wire down upon said core, applyng a second coating of mobile setting material to the core, wire, and folded portions of the end connectionelements, and setting said second coatin 3. The method of making an insulated electric resistance element which comprises the following steps, providing a tubular core of unglazed porcelain, chami'ering each end of said core, resiliently engaging one end of said end connection elements upon the ends of said core each with a portion projecting radially therefrom, applying a first vitreous enamel coating in mobile condition leaving parts of said end connection elements exposed, firing said first coating, winding resistance wire on said core upon the hardened first coating and conductively joining it to the exposed parts of the radially extending portions of said and elements, folding said radially extending parts and joined portionsof wire down upon said chamfered portion oi. the core, applying a second coating of vitreous enamel to the core, wire, and folded portions of the end connection elements. and firing said second coating.

4. An insulated electric resistance element comprising, in combination, a tubular core of insulating material; a metallic end connection having an end protuberance wedgingly engaging in the hollow end of said tubular core, and a second protuberance projecting in a substantially radial plane; an adherent hardened undercoating of insulating material on said core, said first named protuberance, and all but a small portion of said secondprotuberance; resistance wire wound on said core upon the hardened coating, means conductively connecting said wire to the uncoated part of said second protuberance of said end connection, said protuberance and wire connection folded down snugly upon said core adjacent an end thereof; and a top layer of insulating material applied to the surfaces of all of said named parts with th exception of the extreme end of said end connection.

accuses 5. An insulated electric resistance element :omprising, in combination, a tubuiar core of unzlazed porcelain having at least one of its ends :hamiered, a metallic end connection having an a and protuberance wedgingly and resiliently en- 5 aged in a hollow end oi the tubular core and a lecond protuberance projecting in a radial plane, r coating of vitreous enamelfired onto said core ind said end connection with the exception of :he extreme and of the latter and. at a portion.

)I said second protuberance, resistance wire wound onto said fixed coating upon the core, neans conductivcly connecting said wire with ;he exposed part of said second protuberance,

said second protuberance and the wire connection folded snugly down upon the core upon the :hamiered portion of the end thereof, and atop :oating of vitreous enamel fired onto the whole element except for the extreme end of said end :onnection.

and extending diametrically of said recess, re-

sistance wire wound on said core, and a unitary metallic end connection element; said end consection element comprising a straight elongated strip One end of which is adapted to be connected in a circuit to which the resistance element is to so be applied, and the opposite end of which is wedgingly engaged within said recess in the end of said core, and a transverse metallic strip rigidly and conductively connected to said elongated strip, said transverse strip extending radially of said core within said keri at the end thereof; and means conductively connecting said wire to the radially outer end of said transverse strip.

7. The method 0! making an insulated electric resistance element which comprises the following steps, providing a core of tubular insulating material engaging a metallic end connection within each end 01' said tubular core, applying a first mobile insulating setting coating to the core and the greater portion of the and connections leaving certain parts or the latter exposed, setting the coating, winding resistance wire on said first coating, conductively joining said wire to the uncoated parts or the end connections, applying a second mobile insulating setting coating to the 5 core, the first coating, the resistance wire, and the end connection and setting said second coating, said metallic end connection being made by spot welding a transverse metallic strip on to a longitudinal metallic member: said longitudinal metal: lic. member affording the means for coupling the completed resistance element in an electric circult.

8. The method of making an insulated electric resistance element which comprises the following steps, providing a core of insulating material having an axial recess in at least one end thereof, forming a transverse kerf traversing the end of said core and extending diametrically of said recess, engaging'a metallic end connection with-' in saidrecess, said. end connection comprising a straight elongated strip one end of which is adopted to be connected in'a circuit to which the resistance element is to be applied, and the opposite end of which is wedgingly engaged within said recess, and a transverse metallic strip rigidly and conductively connected to said elongated strip and extendingradially of said core within said kerf, applying a first mobileinsulating setting coating to the core and the greater'portion of the end connections leaving certain parts of the latter exposed, setting the coating. winding resistance wire on said firstcoating, conductively joining said wire to the uncoated. parts of the end connections, applying a second mobile insulating setting coating to the core, the first coating, the resistance wire, and the end connections and setting said second coating. I

The following references are of record in the file of thispatent:

UNITED STATES PATENTS Number Name Date 1,563,812 Waller Dec. 1, 1925 1,608,005 Schoeppler Nov. 23, 1926 1,942,496 Siegel Jan. 9, 1934 1,963,755 Mead June 19, 1934 2,195,705 Morgan Apr. 2, 1940 FOREIGN PATENTS Number Country Date 177,622, Australia Oct. 12, 1943 239,926 Great Britain Sept. 17, 1925 475,667 Great Britain Nov. 24, 1937 Great Britain Jan. 27, 1939 

